To effect motor-driven changes of modes and programs (tape travelling directions) in a tape player, an arrangement is required where driving power from a motor is transmitted to individual mechanisms only upon mode or program changes. An arrangement which has been used in the prior art for this purpose includes an intermittent gear wheel located near a continuously rotating drive gear wheel. In a normal condition of the tape player where no change is desired, the intermittent gear wheel is locked unrotatable at a position where a cutout partly breaking a series of teeth along the outer circumference of the intermittent gear wheel is opposed to the drive gear wheel so that no rotation is transmitted to the intermittent gear wheel. Upon any change of modes or programs, the intermittent gear wheel is unlocked, and the series of teeth thereof engages the drive gear wheel so that the rotation of the motor is thereafter transmitted to other members via the intermittent gear wheel.
FIG. 2 shows a prior art arrangement of such an intermittent gear wheel mechanism which includes an intermittent gear wheel with two cutouts along the outer circumference thereof so that a change plate for channel changing operation is reciprocated by every half revolution of the intermittent gear wheel.
More specifically, the intermittent gear wheel 61 is rotatable about an axle 62 and engageable with the drive gear wheel 63 located at a fixed position and driven by a motor (not shown) of the tape player. The intermittent gear wheel 61 has two symmetrical cutouts 64a, 64b partly breaking a series of teeth along the outer circumference thereof. On one surface of the intermittent gear wheel 61 are provided two symmetrical engaging portions 65a, 65b associated with the cutout 64a, 64b.
A pin 66 is formed on the surface of the intermittent gear wheel 61 and received in an elongated hole 68 formed in the change plate 67.
Near the intermittent gear wheel 61 is provided an L-shaped lock link 70 pivotable about an axle 69. One extension of the lock link 70 has a hook-shaped lock portion 71 at the distal end thereof for engagement with the engaging portions 65a, 65b. A spring 72 biases the lock link 70 to bring the lock portion 71 to an engageable position. The other extension of the lock link 70 has a pin 73 at the distal end thereof which is pushed by a push portion 75 of an unlock lever 74 when the lever 74 is inserted.
Opposite to the lock link 70 is mounted a sub-lock link 77 pivotably about an axle 76. A spring 72 biases the sub-lock link 77 in a direction for bringing a lock portion 78 at one distal end of the link 77 into engagement with the engaging portions 65a, 65b of the intermittent gear wheel 61. The other distal end of the sub-lock link 77 is provided with a pin 79 with which a push portion 80 of the unlock lever 74 engages to bias the sub-lock link 77 in a releasable direction against the energy of the spring 72.
The unlock lever 74 is always biased in a withdrawal direction by a spring 81.
In a normal operation of the prior art arrangement, since the lock portion 71 of the lock link 70 engages the engaging portion 65a due to the energy of the spring 72, the intermittent gear wheel 61 is locked at an angular position where the cutout 64a faces the drive gear wheel 63. Therefore, the intermittent gear wheel 61 is unrotatable regardless of rotation of the drive gear wheel 63, and no program change is effected.
On a channel change, when the unlock lever 74 is compressed, the push portion 75 thereof pushes the pin 73 and rotates the lock link 70 against the energy of the spring 72. Thereby the lock portion 71 is detached from the engage portion 65. The intermittent gear wheel 61 is now allowed to slightly rotate with a priming force applied thereto from the change plate 67, and the circumferential teeth thereof engage the drive gear wheel 63. After this, the intermittent gear wheel 61 is rotated by the drive gear wheel 63, and the pin 66 of the gear wheel 61 received in the elongated hole 68 moves the change plate 67 upward. Thereby a known channel changing mechanism is activated.
The unlock lever 74 is now allowed to return with the energy of the spring 81, and the push portion 75 thereof is detached from the pin 73. With a subsequent half revolution of the intermittent gear wheel 61, the second engaging portion 65b engages the lock portion 71, and the intermittent gear wheel 61 is locked again at an angular position where the second cutout 64b faces the drive gear wheel 63. As a result, no rotation is transmitted from the drive gear wheel 63, and the change plate 67 comovable with the intermittent gear wheel 61 is locked until a subsequent operation by the unlock lever 74.
In the prior art lock mechanism described above, if the unlock lever 74 remains at the inserted position, the lock link 70 is continuously pushed and cannot bring the lock portion 71 into engagement with the engaging portion 65b. Therefore, the intermittent gear wheel 61 continues rotation after the cutout 64b reaches the drive gear wheel 63, and the change plate 67 once having moved returns to its original position.
To prevent such an overrun of the intermittent gear wheel 61, an improved prior art mechanism employs the sub-lock link 77 which is rotated in an engageable direction by the spring 72 while the unlock lever 74 is inserted, so that the lock portion 78 of the sub-lock link 77 lockingly engages the engaging portion 65a which failed to engage the lock portion 71 of the lock link 70.
After the unlock lever 74 withdraws, the push portion 80 thereof rotates the sublock link 77 against the energy of the spring 72 so as to detach the lock portion 78 from the first engaging portion 65a. Regardless of the release of the sublock link 77, since the lock portion 71 of the lock link 70 immediately engages the second engaging portion 65b due to the withdrawal of the lever 74, the intermittent gear wheel 61 cannot rotate before it engages the drive gear wheel 63.
The improved prior art mechanism certainly has the advantage that no error will occur during channel changing operation, because the intermittent gear wheel 61 never fails to stop after a half revolution regardless of non-return of the unlock lever 74. However, the use of two lock links invites a complicated structure of the mechanism. In particular, timely control of two lock links with respect to insertion of the unlock lever to establish reliable engagement or disengagement with respect to the engaging portions of the intermittent gear requires a more difficult design and accuracy of the mechanism.